Production of metallic magnesium by ferrosilicon reduction



Patented Mead, 1945 'unirsp srAras orricsds amazes PRODUCTION OF METALLIC MAGNESIUM BY w I FERROSILICON REDUCTION o Leslie Victor Whiton and Hugh McLaurin Weld,

- Haley, Ontario, Canada, assignors to Dominion Magnesium Limited, Toronto, Ontario, Canada, a corporation of the Province of Ontario No Drawing. 6 Application October 27,1943, sol-m No. 507,882. In Canada October 1:, 1m

metallic magnesium by thermal reduction of volatilize the magnesium and condense the latter in dense coherent structural form. The vapours evolved from the charge are condensed in a portion of each retort extending outside the furnace and within which is located removable condenser sleeve for removal with the condensed magnesium. Means may be provided for the condensation and independent removal of metals having a ratio of calcine to silicon of 1 to 0.132, thatis an excess of calcine. as well as the theoretical ratio have been used.

An object of the present invention is to imfprove the overall economic efllciency of this method. A more specific object is to obtain a maximum recovery of magnesium in the calcine ered.

a higher vapour pressure than magnesium.

While the retort remain within the furnace under operating temperatures of 1100 to 1200 C. the condenser end of each retort is opened to the air for removal of the condensed metal, discharge of the residue and recharging. The retorts may be 6 to 12 inches in diameter, preferably 8 'or 10 inches, and are charged and discharged in groups in an operating cycle which may vary from say 6 to 12 hours.

During the operating cycle the hot retorts are charged with briquettes, evacuated to remove steam, occluded and adsorbed gase and the charge is maintained under avery low pressure.

of say 0.02 mm. Silicon vapour is evolved from the ferrosilicon and this vapour reduces the magnesia to magnesium which is volatilized and condensed. At the end of the cycle when the magnesium has been volatilized and condensed the exposed ends of the retorts are opened to the air and discharged.

-It is known that the reaction proceeds best when lime is.present with the magnesia. The theoretical equation representing the reaction is as follows:

It has been found that greatly improved results are obtained by using 110 to 130% of the theoretical amount of silicon required for the reaction. The invention thus contemplates using a ratio of calcine to silicon within the range'of 1 to 0.160 and 1 to 0.189. Best results have been obtained by using 115% of the theoretical amount of silicon, that is a ratio of calcine to silicon of 1 to 0.167.

It is known that commercial ferrosilicon may contain varying amounts of silicon and due regard must be given to the actual silicon content of the .ferrosilicon used when determining the amount to be employed in providing the desired ratio of calcine to silicon.

It appears that the increased concentration of ferrosilicon in the briquettes charged into the retorts causes a more rapid transfer of heat into and throughout the charge. Thus in a given period of time the chargeabsorbs a greater amount of heat and the temperature more quickly reaches the'eiiective reaction point. Also with thegreater concentration of ferrosllicon the concentration of silicon vapour is increased to cause the reacton' to go forward to more completely reduce the magnesia and liberate the metal.

cycle the increase in the amount of magnesium recovered from the. charge was 26.3%. as compared with the former practice in which a ratio of calcine to silicon of 1 to 0.132 was used.

Using a ratio of calcine to silicon of 1 to 0.167" in an operating cycle of 10. hours the amount of magnesium recovered was increased by 37.5% as compared with the former. practice. That is to say. the amount of silicon required per pound of magnesium recovered was only 91.9% ,of that previously used. At the same time the h'eat'requirements of the iurnace per pound of magnesium recovered was reduced by about 20%.

Moreover the structures; or so-called crowns, of magnesium formed in the condenser are heavier and more compact with greater mechanical strength. As a result fewer fines are produced in handling the crowns. there is a reduction in melting los and in flux consumption in melting the crowns and casting the metal into ingots.

We claim: I

I. In the production of magnesium by thermal reduction of magnesia-containing materialwith ferrosilicon the step which comprises heating in a retortunder-reducing conditions briquettes comprising the magnesia-containing material and ferrosilicon in proportions to provide 110 to 130% of the theoretical amount of silicon for the reaction.

2. A method as defined in claim 1 wherein calcined dolomite is mixed with ierrosilicon in proportions to provide at least 10 and not more than 30% of silicon in excess of the theoretical amount required for the reaction.

Accordingly,

2,870,898 v 3. A method of producing metallic magnesium which comprises calcining dolomite; and heating under reducing conditions thefcaicined dolomite with ierrosilicon in proportions to provide aratio of calcine to silicon between I to 0.160 and 1'toO.189. L

4. A method of recovering magnesium'from' magnesia-containing material which comprises the step of heating under reducing conditions the magnesia-containing material with ierrosilicon proportions to provide substantially 15% silicon in excess oi the theoretical amount required for the reaction.

5. A method of recovering magnesium from magnesia-containing material by thermal reduction which comprises heating under reducing conditions said material containing one mole of VICTOR'WHITON. 4 HUGH MQLAURIN'WELD. 

